The present invention relates to froth flotation processes for recovery of metal values from base metal sulfide ores. More particularly, it relates to improved sulfide collectors comprising certain substituted mercaptobenzothiazole compounds which exhibit excellent metallurgical performance over a broad range of pH values.
Froth flotation is one of the most widely used processes for beneficiating ores containing valuable minerals and is described in U.S. Pat. No. 4,584,097, hereby incorporated herein by reference.
The success of a sulfide flotation process depends to a great degree on the reagent(s) called collector(s) that impart(s) selective hydrophobicity to the value sulfide mineral that has to be separated from other minerals. Thus, the flotation separation of one mineral species from another depends upon the relative wettability of mineral surfaces by water. Typically, the surface free energy is purportedly lowered by the adsorption of heteropolar collectors. The hydrophobic coating thus provided acts in this explanation as a bridge so that the mineral particles may be attached to an air bubble. The practice of this invention is not, however, limited by this or other theories of flotation.
Xanthates, dithiophosphates, alkyl xanthogen alkyl formates, bis alkyl xanthogen formates, dialkylthionocarbamates, hydrocarboxycarbonyl thionocarbamates, etc. have been shown to be useful collectors in froth flotation procedures. Most of these known collectors, however, are known to suffer from at least one deficiency which prevents them from being used universally for the recovery of metals from each and every ore requiring refining, such as pH dependency, affinity for some metals versus others etc.
The use of substituted mercaptobenzothiazoles as collectors for the recovery of lead and zinc oxides and carbonates is taught in U.S. Pat. No. 4,724,072. The collectors thereof are taught as capable of forming water-insoluble compounds with metals, the metal ion being bonded to the ionic molecule of the collector through ionic bonds as well as through a donor-type bond. The association between the metal and the collector occurs so that the coordination number and the electric charge of the metal are balanced respectively by the sum of the donor groups and of the ionic charge of the collector with which the metal combines.
The mechanism of adsorption of various mercaptobenzothiazoles on oxide or carbonate minerals is quite different from that on sulfide minerals. In sulfide systems, i.e. as per the instant invention, irrespective of the surface complex formed, the substituted mercaptobenzothiazoles must go through an oxidation step. The oxidation products (a dimer and/or metal thiazole complex) are the adsorbing species on minerals, such as pyrite, chalcopyrite, chalcocite or galena. The substituted mercaptobenzothiazoles oxidize more readily than other similar structures under a given set of conditions. This is attributable to the electron-donating tendency of the substituent group on the ring. The overall result is that the substituted mercaptobenzothiazoles are better collectors than mercaptobenzothiazole in flotation of sulfide minerals.
Accordingly, it is an object of the present invention to provide an improved sulfide collector and flotation process for the beneficiation of sulfide minerals employing froth flotation methods for the recovery of metals from ore, especially gold and silver.